1. Technical Field of the Invention
The present invention relates to a method for use of a retrievable well plug according to claim 1. Further, the invention relates to a retrievable well plug device according to the introduction of claim 4. Further, the invention relates to a well plug anchoring device to keep the well plug in position under pressure according to claim 17.
2. Background of the Invention
Well plugs are used, for example, for zone isolation of oil and gas wells. Such well plugs often have an expandable packer element made of elastic rubber, which seals the well bore for fluid and pressure, and an expandable anchoring device, which is used to hold the well plug in position under pressure. Often, the well plug must pass narrower sections in oil and gas well bores, such as valves and nipples, for thereafter to be set at a wider tube diameter.
Known technology requires use of long well plugs to satisfy these expansion requirements. The prior art is represented by the Norwegian Patents 304615 and 301945 in the name of Bremiteknologiutvikling AS (corresponding to U.S. Pat. No. 6,142,227 and U.S. Pat. No. 6,234,249), describing a retrievable well plug having an upper packer element and a lower packer element connected to each other via a linking-connection. As the packer elements are pushed towards each other, the linking-connection expands radially and makes a mechanical barrier for the packer elements as the packer elements expand axially and results in a tight sealing plug in the well bore. These inventions have features that need to be improved.
The packer concept comprises two symmetrical packer elements making up a seal from each side, and a mechanical barrier therebetween. This concept requires long travel or so-called setting movement to achieve a sufficient expansion for sealing.
The mechanical barrier is made of several expandable linking-pairs fastened to the rest of the plug by means of bolts. Such a fastening device will place restrictions on the number of linking-pairs to be used, and consequently also place restrictions on the sealing quality of the mechanical barrier.
The described well plug uses a split pipe and the abovementioned linking-pairs as a mechanical barrier to cause a plastic deformation for optimum sealing. This can cause problems when the well plug is to be retrieved.
A possible disruption of one of the two symmetrical packer elements can result in a removal of mechanical connection between the upper part of the well plug and the expanding anchoring device. Consequently loosening of the anchoring device at the time of retrieval of the well plug becomes difficult.
The described anchoring device provides a limitation of the expansion of the well plug, and requires a long setting wandering (setting movement) to achieve sufficient anchoring force towards the pipe wall.